Several types of tunable capacitors have been developed for mobile communication applications such as tunable filters, phase shifters, multiplexers, voltage-controlled oscillators and tunable matching networks.
A first type is a semiconductor based tunable capacitor, i.e. PIN diodes, varactor diodes and field-effect transistors (FET's). A second type is a MEMS type tunable capacitor, which has a possibility to gain a large change of capacitance due to change of a distance between electrodes or in plane relative position of the electrodes (an in-plane translation of the bottom or top electrode may result in a change of the effective overlapping area of the capacitor and thus vary the capacitance). A third type is a tunable capacitor using ferroelectric material sandwiched between two electrodes. In that type of capacitor the relative dielectric constant of the ferroelectric material is varied by applying an electric field (which is done by applying a voltage over the electrodes). All three types of tunable capacitors have their own limitations in operational use.
In view of these limitations there is a need for an alternative type of tunable capacitor.